1. Field of the Invention
The present invention is directed to a process for producing stainless steels, and particularly for producing special steels containing chromium and chromium-nickel, in a smelting arrangement having at least two vessels for supplying a steel foundry.
2. Description of the Related Art
Usually, an electric furnace of conventional construction is used in the production of chromium-containing, and chromium-nickel-containing stainless steels. The electric furnace is constructed as a D.C. or A.C. furnace in which scrap and other iron-containing metallic raw material, e.g., pig iron or DRI (Direct Reduced Iron), are melted together with an adequate amount of alloying elements or alloy carriers. The raw or base material which is melted for this purpose is tapped off into a ladle at a temperature of 1670.degree. C. to 1700.degree. C. The ladle is subsequently emptied into a converter wherein the melt, which contains approximately 2.5% carbon and approximately 1% silicon, is first oxidized or refined by oxygen. The carbon content is next reduced by mixtures of oxygen and nitrogen, and later by mixtures of oxygen and argon.
Depending on the application of different process techniques, decarburization is carried out to produce a final carbon content of less than 0.1%. Resulting chromium losses in the slag must then be recovered by reduction with ferrosilicon or secondary aluminum.
Further, it is known in a three-step process technique to tap off the metal from the converter at carbon contents of approximately 0.2% to 0.3% and subsequently to bring the metal to the final carbon content in a separate vacuum oxidation process.
A disadvantage that the previously known methods have in common is that decanting or reladling the melt one or more times results in high temperature losses. These losses must be compensated. For by using a high tapping temperature resulting in a high amount of energy consumption in the primary melting vessel, such as the electric arc furnace. In addition to the high amount of energy consumption, the known methods disadvantageously cause increased electrode and refractory wear in the electric furnace. Furthermore installation of the converter required for the second process step requires substantially high construction heights for a surrounding building in order to accommodate a blowing lance and exhaust gas system.